Having problems connecting my NEST thermostat

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Please do not rate me until we have finished our dialog and you can rate me as excellent service. Thanks for the chance to help. Can you be a bit more specific? What kind of problems? Type of system? What wires and to what terminals do you have connected so far?

I purchased the 2nd generation NEST for my McQuay units in my condo. The McQuay units are controlled by wall thermostats. I have 4 stranded wires...Y (blue), G (green), Rc (red), W (white). I can send a photo of wires connected to original thermostat.

Basically, I am getting an E30 error = no power to Y1. After messing with configuration, I was told by CS that I have stranded wires, and stranded wires don't work with NEST. However, I have searched Google, and others have been able to get the NEST to work with their HVAC with stranded wires.

I would try taking out all the stranded wires and twisting them together into a tight bundle then reinsert them. Sometimes on stranded wires, the wires flatten out and NEST may not think there is a wire inserted into that connector. You may also have issues if the wires are too thin. In this case, you may have to use a wirenut and wire nut a larger wire to each of the smaller ones, then tape with electrical tape. Remember, whenever working with wiring, you should always turn the power to the unit off first.

Have you attached the larger wire to the ends of the smaller thermostat wires? That would be the first thing. Also, check continuity from the Y1 wire from the stat back to the air handler or furnace. Just because it worked before doesn't mean something couldn't have changed. Remember, NEST does not recommend using stranded wire, but sometimes this problem can be overcome by the suggestions I made previously.

Can you verify that the Y wire is connected to Y on the board and that the wire has continuity from the thermostat down to the board? If you have extra unused wires in the thermostat bundle, you may want to try substituting one of those (say, a blue, for example) for the Y wire to see if it's a bad wire or something.

The board is usually found in the lower panel near the blower. Try turning power off and substituting the brown wire for the Y wire (whatever color it is) both at the board and the thermostat, then turn power back on.

Then I have to believe you have a bad thermostat. There is one other thing you can check. With the front part of the NEST thermostat off and the wires exposed, take a voltmeter, set to volts AC and check from the red or R terminal to the Y. You should read 24 volts.

Before you think about replacing thermostat, I found this while looking through questions and answers on the NEST support website. Sometimes the voltage coming off Y or Y1 can be too low for a variety of reasons. They recommend running a common wire. To do this, you would find an unused wire (I think you said you have an unused black), and with furnace power off, connect that black to the C terminal on the board (where all the other thermostat wires attach) and to the C on the NEST thermostat. I'm not saying this will solve your problem, but it's worth a try.

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